Unveiling the Mechanisms of Aeromonas hydrophila COF_AHE51 Induced Mortality in Labeo rohita: Hemato-biochemical and Immune-Pathological Perspectives

Background: This study presents the successful isolation and comprehensive characterization of a selected virulent strain of Aeromonas hydrophila, denoted COF_AHE51, which was identified as the causative agent behind mass fish mortality in an aquaculture pond in Tripura. Methods: The identification of this species was achieved through morphological, biochemical, and molecular techniques. The pathogenicity was assessed by fulfilling Koch’s postulate, determination of haemato-biochemical and immune-pathophysiological parameters and histopathological study. The antimicrobial resistance was examined by performing antibiotic sensitivity test. Result: Experimental infection of Labeo rohita with COF_AHE51 resulted in the development of hallmark clinical signs, such as haemorrhages, abdominal swelling, discoloration, and tail and fin rot. The calculated LD50 of the pathogenic strain was 1.4 x 106 cfu/fish. In-depth hematological and immunological analyses, alongside histopathological examinations of affected tissues, revealed remarkable perturbations suggestive of systemic bacterial septicaemia. Furthermore, the strain was observed to be resistant to several commonly used antibiotics, including kanamycin, cefoxitin, cefotaxime, and ampicillin, accentuating the considerable threat posed by A. hydrophila infections in aquaculture settings.